Fixes CORE232
Change riak_core_sysmon_handler to use hibernation to free up
resources when it is idle since it does not do a good job of freeing
these resources on its own. Also force garbage collection on the
riak_core_sysmon_handler process if it receives a large_heap message
about itself. This is to avoid a feedback loop that can lead to severe
memory usage by the handler, node slowness, and even cause the node to
crash after consuming all available memory.

…roxy.
Fixes CORE231
The call functions in riak_core_vnode_proxy only expected a result
of {ok, Res}. This change calls a new function, call_reply, to
better handle the case when an exception is thrown and wrap
the reason in an error tuple.

Calling `add_supported_to_ring` is not threadsafe.
If a process retrieves the member_meta and then
it's concurrently updated by another process,
the original process' changed will be overwritten.
To exhibit the original bug, I added a
timer:sleep(crypto:rand_uniform(1, 1000))
line inside the spawned fun that calls
riak_core_ring_manager:ring_trans(F, ok)

Fixes riak_core 213
Change riak_core_vnode_worker:handle_work to use gen_server:cast
instead of gen_server:call. This addresses a possible timeout
condition that can result in a vnode worker pool crashing.